Hereinafter, the general term “aircraft” will refer to fixed-wing aircraft as well as to rotary-wing aircraft, that is to say, the term “wing” encompasses the wing of a fixed-wing aircraft as well as the rotor blade of a rotary-wing aircraft. Although in principle, the invention can also be employed for fixed-wing aircraft, only a rotor blade of a rotary-wing aircraft will be examined in greater detail below.
It is a known fact that the rotor system of a helicopter is the main cause of noise and vibrations in the cabin. At the same time, the rotor system also generates a high level of outside noise, particularly during the approach for landing. These noise emissions and vibrations lead to a marked reduction in comfort for helicopter passengers and are also detrimental to the environment. Further developments in helicopter construction are aimed at greatly reducing these noise emissions and vibrations.
In the case of helicopters available on the market with their known rotor systems, the rotor blades are actuated collectively and cyclically by means of a swash plate and a mechanical linkage. The notion has become established to expand this primary rotor-blade control in order to reduce noise emissions and vibrations by using a flap installed in the area of the tip of the individual rotor blade. This flap is meant to allow individual control of the blade. The use of a controllable flap in the area of the blade that generates the uplift, preferably in the vicinity of the blade tip and on the profile trailing edge of the blade, creates the possibility for the rotor blade to continuously adapt to varying flow approach conditions during rotation of the rotor blade. This makes it possible to reduce noise emissions and vibrations caused by the rotor system.
German patent application DE 101 16 479 A1 discloses a rotor blade with a movably mounted flap. The flap is movably attached to the rotor blade by means of anti-friction bearings. The flap is actuated with a flap actuator that is configured in the form of a piezo actuator and that is arranged at a distance in a front area of the rotor blade as seen in the direction of the chord. The piezo actuator transmits its actuating power to the flap via rod-shaped connection elements. Here, the rod-shaped traction elements are mounted by means of appropriate sliding bearings.
With the known rotor blades of the above-mentioned type, the effectiveness of the flap declines and it quickly loses its functionality after a relatively short period of operation because wear and tear of the highly stressed flap bearing soon results in play. This reduces the available excursion range of the flap, the aerodynamic and mechanical flap effect decreases and the friction in the flap bearing is greatly increased. Since the sliding bearing of the rod-shaped traction elements is likewise subjected to friction, the functionality of the piezo actuator is severely impaired. Moreover, the friction has a negative effect on the control and regulation programs needed for a precise adjustment of a movable flap.